Specifically, how do you read this code? I\'m familiar with what CAR and CDR do,

Question

Specifically, how do you read this code? I'm familiar with what CAR and CDR do, but I don't know how to read the conditional statement

5. Let F be the following LISP function (DEFUN F (L) COND (NULL L) NIL) (NULL (CDR L)) (CAR L) ) T (F (CDR L))) The NULL function returns a true value if its argument is an empty list (a) What does F return when passed (A B) as its argument? (b) What does F return when passed (A (B C)) as its argument? (c) What does F return when passed (A B (C)) as its argument? (d) In general, what does F return when passed a list L?

Explanation / Answer

The basic syntax of COND is:

(cond

   ((predicate1) (then do something 1))    ;if this predicate is true,
                                              ;do something 1
      ((predicate2) (then do something 2))    ;if this predicate is true,
                                              ;do something2,
                                              ;each predicate and action
                                              ;following the
                                              ;first one is optional

      (t (else do this))                      ;else, if none of the
                                              ;predicates returns
                                              ;T, do this
)

here predicate1 is NULL L    then NIL

and predicate2 is NULL (CDR L) then CAR L

and the else case is F (CDR L)

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